1. Field of the Invention
The present invention relates to a system for transmitting an optical signal through an optical waveguide containing a fiber-optic amplifier which includes an amplifying length of fiber, a pump source, and a wavelength-selective fiber optic coupler for coupling the pump source to the amplifying length of fiber.
2. Description of the Prior Art
Such a transmission system is known from "ECOC '89", Fifteenth European Conference on Optical Communication, Sep. 10-14, 1989, Gothenburg, Sweden, Proceedings, Vol. 1, Regular Papers, TuA 5-7, pages 86 to 89.
In the above-referenced article, two different system configurations are explained. In the first ("copropagating configuration"), the light from the pump source is launched into the Er.sup.3+ -doped length of fiber via a coupler which, as viewed in the direction of transmission of the optical signal to be amplified, is located in front of the amplifying length of fiber. In the second system configuration ("counterpropagating configuration"), the coupler, as viewed in the direction of transmission of the signal to be amplified, is located beyond the length of fiber.